It's possible that men are directly detecting the higher levels of estrogen during ovulation, said Jim Roney, a scientist at the University of California, Santa Barbara. Equally possible is that men are sensing other chemicals that rise and fall depending on the amount of estrogen. Scientists just don't know.
Despite the remaining unknowns, the new research marks a milestone for smell scientists.
"This is one of the first papers to show (a change in testosterone) in response to a chemical stimulus," said Roney. "It's a new area of research."
For the second experiment, the testosterone levels of the men who smelled the T-shirts of ovulating women were, on average, 15 percent higher than men who sniffed the two other T-shirt samples.
Other studies have linked higher levels of testosterone with an increased in sexual arousal, said Maner. Whether a 37 percent or 15 percent difference in testosterone is enough to affect a man's behavior is unknown.
Another unknown is the whether a man could detect an ovulating women in a real-world situation, say a crowded bar. The two experiments were done under controlled laboratory conditions. Nevertheless, scientists say the experiments could have real world significance for potential love connections.